1. Field of the Invention
This invention relates to the field of offshore or marine wells and operations performed from a platform on the surface of the water, and more particularly it relates to methods for positioning and placing without the use of underwater divers a template or dome used in conjunction with the offshore well.
2. Description of Related Art
Heretofore templates and domes have been used in connection with offshore or marine oil or gas wells. Petroleum wells have been drilled through a sea floor template. See Frank R. Carmichael, Offshore Drilling Technology (Park Ridge: Noyes Data Corporation, 1975), pp. 50-55 and other pages therein. Templates have also been known as guide bases since templates act as a guide for equipment such as the oil or gas well production tree as well as providing a guide base for mounting of the platform or vessel on the surface of the water. The purpose of the template is to provide correct spacing between the wells in order that they will line-up with the conductor guides in the platform jacket.
Prior to the present invention the placement or the orientation of templates to the desired heading was relatively inaccurate and required the assistance of underwater divers. Typically, a template would be suspended by steel cables or chains from the end of a drill string extending beneath the surface vessel. The drill string would be lowered until the template reached the proximity of the sea floor and then the divers, using magnetic compasses, would man-handle the template until it was in the approximate orientation relative to the desired magnetic or true bearing. Following the shoving of the template into position, the drill string would be further extended until the template rested upon the sea floor when the divers would then be called upon to disconnect the template from the drill string. Because this operation is frequently conducted at water depths in excess of 300 feet or 100 meters, the time available for the divers to operate at that depth was limited. Moreover, the template and drill string, which are metal, would tend to influence magnetic compasses reducing the accuracy of the orientation. Normally, this type of prior operation resulted in the placement of the template only within five (5) degrees to fifteen (15) degrees of the desired heading.
It was also known to place a gyroscopic device down a drill string through its inner bore to determine the orientation of a tool or element mounted near the end of the drill string. The gyroscope would determine the orientation of the tool or element when the end of the drill string is at some distance from the surface vessel.
With the present invention underwater divers are not required and thus reduces the amount of time needed for this operation and eliminates an added expense. Moreover, the orientation of the template when placed using the present invention is accurate to within one (1) degree of the desired heading.
Nelson et. al., U.S. Pat. No. 3,353,595, relates to methods and apparatus for completing offshore wells in which the wellhead is located at an underwater level. It is of interest for its disclosure of J-slots 29.
Fowler, U.S. Pat. No. 3,732,923, discloses a method and apparatus for remotely connecting flowlines to an underwater wellhead, and Walker, U.S. Pat. No. 4,126,183 teaches an offshore well apparatus with a protected production system. Both Fowler and Walker disclose a J slot-lug combination in FIGS. 17 and 11 respectively. However, neither patent discloses any means for lowering and orienting a template using such means.
Postlewaite, U.S. Pat. No. 3,302,709, discloses a method for attaching and detaching a working base to an underwater well base and is cited only because of its disclosure of a "bayonet" type latch (see FIG. 28).
Domes have been used in the past to protect a well casing stub from damage as well as to prevent the stub from causing damage to fishing nets. After a well is drilled there is a period of time before the well is put into production. When the drilling vessel leaves, the oil well casing is terminated above the level of the sea floor leaving the oil well casing stub. Geodesic domes are then positioned over the stub for protection. While the orientation of the dome in not as critical as it is for a template, domes were normally placed by a similar method to that used for templates.